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Registering Notification in iPhone SDK 3.0

In the iPhone SDK 3.0, I would like to register for a notification that would alert my app when a certain time is reached. Is it possible? Thanks to

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Assuming you have NSDate

in a variable date

and want to run the method dateIsHere:

on that date, do this:



NSTimer* timer = [[NSTimer alloc] initWithFireDate:date
                                          interval:0.0f
                                            target:self
                                          selector:@selector(dateIsHere:)
                                          userInfo:nil
                                           repeats:NO];
[[NSRunLoop mainRunLoop] addTimer:timer
                          forMode:NSDefaultRunLoopMode];
[timer release];
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Configure NSTimer

that runs the selector every 30 seconds (or whatever granularity you need):

 [NSTimer scheduledTimerWithTimeInterval:30.0 target:self selector:@selector(timerFired:) userInfo:nil repeats:YES];

The selector (method) -timerFired:

will run every thirty seconds and check the hour, minute and second components, triggering a notification if the items match the requested time:

 - (void) timerFired:(NSNotification *)notification {
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSCalendarUnit unitFlags = NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
    NSDate *date = [NSDate date];
    NSDateComponents *dateComponents = [calendar components:unitFlags fromDate:date];
    NSInteger hour =  [dateComponents hour];
    NSInteger min =   [dateComponents minute];
    NSInteger sec =   [dateComponents second];
    if ((hour == kDesiredHour) && (min == kDesiredMinute) && (sec == kDesiredSecond)) {
       [[NSNotificationCenter defaultCenter] postNotificationName:@"kTimeComponentsWereMatched" object:nil userInfo:nil];
    }
 }

You register to listen to this notification in some other class:



 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(doSomething:) name:@"kTimeComponentsWereMatched" object:nil];

Accordingly, you have a method in the same class that does something interesting:

 - (void) doSomething:(NSNotification *)notification {
    // do something interesting here...
 }

You can combine this code if it's all in one class. Or specify target

in NSTimer

to indicate the instance of the class you want to run on selector

.

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I am assuming that you want this timer to fire even when the application is closed. You can use a notification to do this, but you must have a server where the notification was sent.

In addition, the iPhone will pull up a warning to tell the user to open the app, but they might not.

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You have to start by setting the NSTimer to fire on a specific date, and the selector that fires can be whatever you want. There is no need to use NSNotifications.

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You're looking for "Local Notifications", which has been implemented in iOS since version 4.0:

http://developer.apple.com/iphone/library/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008194-CH1-SW1

This should be the correct answer for> = 4.0. For earlier versions, there are probably still only NSNotifications (implementing push is too much of a hassle for most)

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